In 1989, an endotoxin-induced serum activity that induced interferon-γ (IFN-γ) obtained from mouse spleen cells was described (Micallef et al., 1996). This serum activity functioned not as a direct inducer of IFN-γ but rather as a co-stimulant together with IL-2 or mitogens. An attempt to purify the activity from post-endotoxin mouse serum revealed an apparently homogeneous 50–55 kDa protein. Since other cytokines can act as co-stimulants for IFN-γ production, the failure of neutralizing antibodies to IL-1, IL-4, IL-5, IL-6, or TNF to neutralize the serum activity suggested it was a distinct factor. In 1995, the same scientists demonstrated that the endotoxin-induced co-stimulant for IFN-γ production was present in extracts of livers from mice preconditioned with P. acnes (Novick et al., 1992). In this model, the hepatic macrophage population (Kupffer cells) expand and in these mice, a low dose of bacterial lipopolysaccharide (LPS), which in non-preconditioned mice is not lethal, becomes lethal. The factor, named IFN-γ-inducing factor (IGIF) and later designated interleukin-18 (IL-18), was purified to homogeneity from 1,200 grams of P. acnes-treated mouse livers. Degenerate oligonucleotides derived from amino acid sequences of purified IL-18 were used to clone a murine IL-18 cDNA (Novick et al., 1992). IL-18 is an 18–19 kDa protein of 157 amino acids, which has no obvious similarities to any peptide in the databases. Messenger RNAs for IL-18 and interleukin-12 (IL-12) are readily detected in Kupffer cells and activated macrophages. Recombinant IL-18 induces IFN-gamma more potently than does IL-12, apparently through a separate pathway (Novick et al., 1992). Similar to the endotoxin-induced serum activity, IL-18 does not induce IFN-γ by itself, but functions primarily as a co-stimulant with mitogens or IL-2. IL-18 enhances T cell proliferation, apparently through an IL-2-dependent pathway, and enhances Th1 cytokine production in vitro and exhibits synergism when combined with IL-12 in terms of enhanced IFN-γ production (Maliszewski et al., 1990).
Neutralizing antibodies to mouse IL-18 were shown to prevent the lethality of low-dose LPS in P. acnes pre-conditioned mice. Others had reported the importance of IFN-γ as a mediator of LPS lethality in pre-conditioned mice. For example, neutralizing anti-IFN-γ antibodies protected mice against Shwartzman-like shock (Fantuzzi et al., 1998), and galactosamine-treated mice deficient in the IFN-γ receptor were resistant to LPS-induced death (Byrn, 1990). Hence, it was not unexpected that neutralizing antibodies to murine IL-18 protected P. acnes-preconditioned mice against lethal LPS (Novick et al., 1992). Anti-murine IL-18 treatment also protected surviving mice against severe hepatic cytotoxicity.
After the murine form was cloned, the human cDNA sequence for IL-18 was reported in 1996 (Okamura et al., 1995). Recombinant human IL-18 exhibits natural IL-18 activity (Okamura et al., 1995). Human recombinant IL-18 is without direct IFN-γ-inducing activity on human T-cells, but acts as a co-stimulant for production of IFN-γ and other T-helper cell-1 (Th1) cytokines (Okamura et al., 1995). To date, IL-18 is thought of primarily as a co-stimulant for Th1 cytokine production (IFN-γ, IL-2 and granulocyte-macrophage colony stimulating factor) (Izaki, 1978) and also as a co-stimulant for FAS ligand-mediated cytotoxicity of murine natural killer cell clones (Novick et al., 1989).
By cloning IL-18 from affected tissues and studying IL-18 gene expression, a close association of this cytokine with an autoimmune disease was found. The non-obese diabetic (NOD) mouse spontaneously develops autoimmune insulitis and diabetes, which can be accelerated and synchronized by a single injection of cyclophosphamide. IL-18 mRNA was demonstrated by reverse transcriptase PCR in NOD mouse pancreas during early stages of insulitis. Levels of IL-18 mRNA increased rapidly after cyclophosphamide treatment and preceded a rise in IFN-γ mRNA, and subsequently diabetes. Interestingly, these kinetics mimic that of IL-12-p40 mRNA, resulting in a close correlation of individual mRNA levels. Cloning of the IL-18 cDNA from pancreas RNA followed by sequencing revealed identity with the IL-18 sequence cloned from Kupffer cells and in vivo pre-activated macrophages. Also NOD mouse macrophages responded to cyclophosphamide with IL-18 gene expression while macrophages from Balb/c mice treated in parallel did not. Therefore, IL-18 expression is abnormally regulated in autoimmune NOD mice and closely associated with diabetes development (Novick et al., 1992).
IL-18 plays a potential role in immunoregulation or in inflammation by augmenting the functional activity of Fas ligand on Th1 cells (Conti et al., 1997). IL-18 is also expressed in the adrenal cortex and therefore might be a secreted neuro-immunomodulator, playing an important role in orchestrating the immune system following a stressful experience (Chater, 1986).
In vivo, IL-18 is formed by cleavage of pro-IL-18, and its endogenous activity appears to account for IFN-γ production in P. acnes and LPS-mediated lethality. Because of its activity, blocking the biological activity of IL-18 in human disease is a therapeutic strategy in many diseases. This can be accomplished using soluble receptors or blocking antibodies to the cell-bound IL-18 receptor.
Cytokine binding proteins (soluble cytokine receptors) correspond to the extracellular ligand binding domains of their respective cell surface cytokine receptors. They are derived either by alternative splicing of a pre-mRNA, common to the cell surface receptor, or by proteolytic cleavage of the cell surface receptor. Such soluble receptors have been described in the past, including among others, the soluble receptors of IL-6 and IFN-γ (Nakamura et al., 1989), TNF (Dao et al., 1996; Engelmann et al., 1989), IL-1 and IL-4 (John, 1986), IFN-α/β (Mizushima and Nagata, 1990) and others. One cytokine-binding protein, named osteoprotegerin (OPG, also known as osteoclast inhibitory factor—OCIF), a member of the TNFR/Fas family, appears to be the first example of a soluble receptor that exists only as a secreted protein (Anderson, 1997; Bollon, 1980). The present invention deals with soluble IL-18 binding proteins.
Recently, it has been suggested that the interleukin IL-18 is involved in the progression of pathogenicity in chronic inflammatory diseases, including endotoxin shock, hepatitis, and autoimmune-diabetes (Kahiwamura and Okamura, 1998). A further indication of a possible role of IL-18 in the development of liver injury resulted from experiments published by Tsuij et al. (Tsuij et al., 1999), showing an elevated level of IL-18 in lipopolysaccharide-induced acute liver injury in a mouse model. However, the mechanism of the multi-functional factor IL-18 in the development of liver injury has not been elucidated so far.
Liver damage or injury may have diverse causes. It may be due to viral or bacterial infections, alcohol abuse, immunological disorders, or cancer, for example.
Viral hepatitis, due to Hepatitis B virus and Hepatitis C virus, for example, are poorly managed diseases that afflict large number of people worldwide. The number of known hepatitis viruses known is constantly increasing. Apart from Hepatitis B and C virus, at least four other viruses causing virus-associated hepatitis have been discovered so far, called Hepatitis A, D, E and G-Virus.
Alcoholic liver disease is another widespread disease associated with chronic consumption of alcohol. Immune hepatitis is a rare autoimmune disease that is poorly managed. Liver injury also includes damages of the bile ducts. Primary biliary cirrhosis (PBC) is an autoimmune liver disease characterized by destruction of the intrahepatic bile ducts.
Several studies have demonstrated that damage to the liver in diseases such as alcoholic hepatitis, liver cirrhosis, viral hepatitis and primary biliary cirrhosis is associated with T-helper cell-1 (Th1) responses. In one study, a novel liver injury model was established in mice by targeting of ovalbumin-containing liposomes into the liver, followed by adoptive transfer of ovalbumin-specific Th1 cells. Combined treatment of mice with ovalbumin-containing liposomes and Th1 cell transfer caused an increase in serum transaminase activity that was paralleled with an elevation of serum IFN-γ levels. In sharp contrast, ovalbumin-specific Th2 cell transfer resulted in an increase of serum IL4 levels but did not induce liver injury. The liver injury was blocked by anti-IFN-γ antibodies and anti-tumor necrosis factor (TNF)-α antibodies. These findings indicate that Th1 cells are the major effector cells in acute liver injury (Nishimura and Ohta, 1999) In another set of studies it was shown that mice over-expressing IFN-γ exhibit spontaneous hepatitis without any pathogen or any other stimulant (Okamoto et al., 1998).
Another study implicated Th1 responses in primary biliary cirrhosis (PBC). PBC is an autoimmune liver disease characterized by destruction of the intrahepatic bile ducts. It is generally believed that cellular immune mechanisms, particularly involving T cells, result in this bile duct damage. The relative strength of Th1 and Th2 responses has recently been proposed to be an important factor in the pathophysiology of various autoimmune diseases. In this study, the The subset balance in PBC was evaluated by detection of cytokines specific to the two T-cell subsets, i.e., IFN-γ for Th1 cells and IL-4 for Th2 cells. IFN-γ and IL-4 messenger RNA (mRNA) positive cells ere counted in liver sections from 18 patients with PBC and 35 disease controls including chronic active hepatitis C, extrahepatic biliary obstruction, and normal liver, using nonisotopic in situ hybridization and immunohistochemistry. Mononuclear cells expressing IFN-γ and IL4 mRNA were aggregated in inflamed portal tracts in PBC livers, but were rarely present in extrahepatic biliary obstruction, alcoholic fibrosis, or normal liver sections. The IFN-γ and IL4 mRNA positive cells in PBC livers were detected in significantly higher numbers than in control livers (P<0,01). Moreover, IFN-γ mRNA expression was more commonly detected than IL4 expression in PBC livers, and the levels of IFN-γ mRNA expression were highly correlated with the degree of portal inflammatory activity. IFN-γ mRNA-positive cells were detected primarily around damaged bile ducts that were surrounded by lymphoid aggregates. The data indicate that Th1 cells are the more prominent T-cell subset in the lymphoid infiltrates in PBC (Harada et al., 1997).
The cytokine pattern on viral antigen recognition is also believed to exert a profound influence on the resolution of viral infections and viral clearance. One study investigated whether a cytokine imbalance oriented toward Th2 type response plays a role in chronic hepatitis B. Cytokine profiles of peripheral blood mononuclear cells associated with chronic hepatitis B were analyzed by RT-PCR. Upon hepatitis B surface antigen (HbsAg) stimulation, expression of IFN-γ, IL-2, IL4, and IL-10 was detected in 41%, 8%, 41%, and 50% of the patients, respectively. Among these cytokines, the expression of the Th1 cytokine IFN-γ was associated with high levels of serum AST/ALT (Aspartate aminotransferase/Alanine aminotransferase), representing typical markers of liver damage. Th2 type cytokines were not shown to exert a protective effect on hepatocytes. In conclusion, production of a Th1 cytokine, IFN-γ, by HBsAg-reactive cells was associated with hepatocyte damage in chronic hepatitis B (Lee et al., 1999). High levels of the FAS ligand and its receptor (CD95) were reported in liver of hepatitis B patients (Luo et al., 1997). FAS ligand is considered to be one of the major cytotoxic agents leading to hepatocyte apoptosis.
Another study identified factors associated with the progression of liver injury in 30 hepatitis C virus/RNA (HCV/RNA)-positive untreated patients with chronic hepatitis. Necroinflammatory and architectural damage were evaluated using Ishak's score. Activated hepatic stellate cells (HSC) were visualized by immunohistochemistry for α-smooth muscle actin (αSMA) and quantitated by morphometry. Plasma HCV/RNA was evaluated using a competitive RT-PCR method. To study the type of immune response involved in the progression of liver injury, IFN-γ-positive cells (as expression of a Th1-like response) were evaluated by immunohistochemistry and quantitated by morphometry. It was found that HSC were mostly detected to areas of lobular necroinflammation or lining fibrotic septa. The αSMA- and Sirius Red-positive parenchyma correlated significantly with necroinflammatory and architectural scores. IFNγ-positive cells were detected in periportal areas associated with the inflammatory infiltrates and significantly correlated with architectural damage. It was therefore concluded that HSC activation and progression of liver injury are associated with a Th1-like response (Baroni et al, 1999). Similarly to the case of Hepatitis B, FAS ligand and its receptor were found in liver and sera of hepatitis C patients (Hiramatsu et al, 1994; Okazaki et al, 1996; Lio et al., 1998)
Th1 cytokines and other Th1 markers were found to be associated with alcoholic hepatitis and liver cirrhosis. Inflammatory stimuli and lipid peroxidation activate nuclear factor κ B (NF-κB) and upregulate proinflammatory cytokines and chemokines. In one study, the relationship between pathological liver injury, endotoxemia, lipid peroxidation, and NF-κB activation and imbalance between pro- and anti-inflammatory cytokines was evaluated. Rats (5 per group) were fed ethanol and a diet containing saturated fat, palm oil, corn oil, or fish oil by intragastric infusion. Dextrose isocalorically replaced ethanol in control rats. Pathological analysis was performed and measurements of endotoxin were taken, lipid peroxidation, NF-κB, and messenger RNA (mRNA) levels of proinflammatory cytokines (TNFα, IL-1beta, IFN-γ, and IL-12), C-C chemokines (regulated upon activation, normal T cell expressed and secreted [RANTES], monocyte chemotactic protein [MCP]-1, macrophage inflammatory protein [MIP]-1-α), C-X-C chemokines (cytokine induced neutrophil chemoattractant [CINC], MIP-2, IP-10, and epithelial neutrophil activating protein [ENA]-78), and anti-inflammatory cytokines (IL-10, IL4, and IL-13). Activation of NF-κB and increased expression of proinflammatory cytokines C-C and C-X-C chemokines was seen in the rats exhibiting necroinflammatory injury (fish oil-ethanol and corn oil-ethanol). These groups also had the highest levels of endotoxin and lipid peroxidation. Levels of IL-10 and IL-4 mRNA were lower in the group exhibiting inflammatory liver injury. Thus, activation of NF-κB occurs in the presence of proinflammatory stimuli and results in increased expression of Th1 proinflammatory cytokines and chemokines (Naji et al., 1999). FAS ligand and its receptor are also elevated in alcoholic liver diseases, suggesting once again that Th1 cytokines are involved in the autoimmune processes induced in alcoholic hepatitis (Galle et al., 1995; Taieb et al, 1998; Fiore et al., 1999).
TNF-α has also emerged as a common pathway in the pathogenesis of alcohol-related hepatic necro-inflammation. Increased levels of hepatic and serum TNF have been documented in animal models of alcoholic liver disease and in human alcoholic liver disease. This dysregulated TNF metabolism has been postulated to play a role in many of the metabolic complications and the liver injury of alcoholic liver disease (Grove et al., 1997; McClain and Cohen, 1989). For instance it was found in one study that patients with alcoholic hepatitis had higher TNF-α levels (mean, 26.3 ng/L; 95% Cl, 21.7 to 30.9) than normal subjects (6.4 ng/L; Cl, 5.4 to 7.4). Patients who subsequently died had a higher TNF-α level (34.7 ng/L; Cl, 27.8 to 41.6) than survivors (16.6 ng/L; Cl, 14.0 to 19.2). In patients with alcoholic hepatitis, TNF-α levels correlated positively with serum bilirubin (r=0.74; P=0.0009) and serum creatinine (r=0.81; P=0.0003). Patients with alcoholic hepatitis had higher TNF-α levels than patients with inactive alcoholic cirrhosis (11.1 ng/L; Cl, 8.9 to 13.3) and severely alcoholic persons without liver disease (6.4 ng/L; Cl, 5.0 to 7.8). Patients with abnormal renal function had lower TNF-α levels (14.1 ng/L; Cl, 5.4 to 22.8) than patients with alcoholic hepatitis. It was therefore concluded that elevations in TNF-α in alcoholic hepatitis are most marked in severe cases, suggesting that TNF-α plays a role in the pathogenesis (Bird et al., 1990)
TNF mediates many of the biologic actions of endotoxin. Recent studies have shown that TNF administration may cause liver injury and that TNF may mediate the lethality of the hepatotoxin galactosamine. One of the most potent TNF inducers is endotoxin. Because patients with alcoholic liver disease frequently have endotoxemia and because many of the clinical manifestations of alcoholic hepatitis are known biologic actions of TNF, its activity was evaluated in patients with alcoholic hepatitis. Basal and lipopolysaccharide-stimulated TNF release from peripheral blood monocytes, a major source of TNF production, was determined in 16 patients with alcoholic hepatitis and 16 healthy volunteers. Eight of 16 alcoholic hepatitis patients and only two of 16 healthy volunteers had detectable spontaneous TNF activity (p less than 0.05). After lipopolysaccharide stimulation, mean monocyte TNF release from alcoholic hepatitis patients was significantly increased to over twice that of healthy controls (25.3+/−3.7 vs. 10.9+/−2.4 units per ml, p less than 0.005). It was therefore concluded that monocytes from alcoholic hepatitis patients have significantly increased spontaneous and lipopolysaccharide-stimulated TNF release compared to monocytes from healthy volunteers (McClain and Cohen, 1989.
Lipopolysaccharide (LPS)-binding protein (LBP) and CD14 play key intermediary roles in the activation of cells by endotoxin. Gut-derived LPS has been postulated to participate in promoting pathological liver injury in alcoholic liver disease. It was demonstrated that rats fed intragastrically with ethanol in oil for 4 weeks had elevated levels of CD14 and LBP in their Kupffer cells and hepatocytes, respectively. Expression of CD14 mRNA was also elevated in nonmyeloid cells. Enhanced LBP and CD14 expression rapidly increases the LPS-induced expression of various pro-inflammatory cytokines and correlates with the presence of pathological liver injury in alcoholic liver injury (Su et al., 1998; Lukkari et al., 1999).
IL-6 is a 26 kd cytokine that plays a major role in the acute phase response, especially the hepatic aspects of the acute phase response. Patients with alcoholic hepatitis manifest many aspects of the acute phase response. Serial plasma IL-6 levels in 30 consecutive patients with moderate to severe alcoholic hepatitis was measured during 6 month. Mean admission plasma IL-6 activity was markedly increased (49.8+/−8.5 U/ml, normal less than 5 U/ml) in patients with alcoholic hepatitis, and levels decreased with clinical improvement to 15.6+/−6.1 U/ml at 6 months. Admission IL-6 activity correlated significantly (r=0.82) with the severity of liver disease as assessed by the discriminant function of Maddrey. IL-6 activity fell over time in a pattern similar to that of bilirubin and C-reactive protein. This and additional studies suggest that plasma IL-6 is probably a marker of inflammation and severity of disease in alcoholic hepatitis (Sheron et al., 1991; Hill et al., 1992).
IL-8, a cytokine produced by a number of cells, including monocytes, macrophages, Kupffer cells and hepatocytes, can activate neutrophils. Peripheral neutrophilia and liver neutrophil infiltration are frequently noted in patients with alcoholic liver disease. It was found that serum IL-8 levels were markedly elevated in patients with alcoholic hepatitis (437+/−51 pg/ml) when compared to all other groups (p<0.05). Levels of IL-8 in patients with alcoholic fatty liver, alcoholic cirrhosis and viral hepatitis were higher than those in controls and in patients with non-alcoholic fatty liver. In addition, IL-8 levels were higher in patients who died (p=0.007), and correlated with biochemical and histological parameters, and severity of liver injury: serum aspartate aminotransferase, alanine aminotransferase, total bilirubin, prothrombin time, indocyanine green retention ratio, TNF-α and peripheral neutrophil count in patients with alcoholic hepatitis. After a 2-year follow up, patients with IL-8 above 479 pg/ml had a higher mortality rate in the alcoholic hepatitis group (p=0.033). These findings suggest that IL-8 as well as some other chemokines are activated in alcoholic liver disease, especially in alcoholic hepatitis, and is closely correlated with liver injury (Martinez et al., 1992; Hill et al., 1992).
Induction of adhesion molecules such as ICAM-1 is associated with the activation and attraction of a special population of inflammatory cells characteristic for alcoholic hepatitis. Frozen liver samples from patients who died with signs of acute alcoholic hepatitis show elevated ICAM-1 expression in the membranes of hepatocytes, as well as the occurrence of CD11b positive polymorphonuclear leukocytes (neutrophils) suggesting a possible major role of the beta 2-integrin Mac-1 as a ligand for ICAM-1. It was concluded that in alcoholic hepatitis cytokines may be responsible for the induction of the adhesion molecule ICAM-1 on hepatocytic membranes and activate a defined population of inflammatory cells, thus contributing to the characteristic histological picture of acute alcoholic hepatitis with its concentration of neutrophils especially in areas with ballooned Mallory body-containing hepatocytes (Afford et al., 1998).
A significant increase in both NK cells (CD3−/CD56+) and the cytotoxic T cells coexpressing the CD3 and the CD56 molecules together with an increased NK cytotoxic activity were observed in patients having alcoholic hepatitis. Interestingly these abnormalities persisted during the withdrawal period (Ohlinger et al., 1993).
Arthritis is a disease involving joint inflammation. The joints show swelling, stiffness, tenderness, redness or warmth. The symptoms may be accompanied by weight loss, fever or weakness. When these symptoms last for more than two weeks, inflammatory arthritis e.g. rheumatoid arthritis may be the cause. Joint inflammation may also be caused by infection, which can lead to septic arthritis. A very common type of arthritis is degenerative joint disease (osteoarthritis). Joint inflammation is not a prominent feature of osteoarthritis.
The medicaments commonly prescribed for arthritis and related conditions are non-steroidal anti-inflammatory drugs (NSAIDs). NSAIDs include aspirin and aspirin-like drugs. They reduce inflammation, which is the cause for joint pain, stiffness and swelling of the joints. However, NSAIDs are unspecific drugs having a number of side effects, involving bleeding of the stomach (Homepage of the Department of Orthopaedics of the University of Washington on Arthritis, Frederick Matsen (Chairman). In addition to NSAIDs, Celebrex™, a cyclooxygenase (COX-2) inhibitor, is used to relieve the signs and symptoms of osteoarthritis and rheumatoid arthritis in adults. It is also indicated for the treatment of patients with familial adenomatous polyposis.
Further, TNF antagonists are used for the treatment of arthritis. TNF antagonists are described, for example, in WO 9103553.
Recent studies indicate that the interleukin IL-18 plays a proinflammatory role in joint metabolism. Olee et al. (1999) showed that IL-18 is produced by articular chondrocytes and induces proinflammatory and catabolic responses. The IL-18 mRNA was induced by IL-1β in chondrocytes. Chondrocytes produced the IL-18 precursor and in response to IL-1 stimulation secreted the mature form of IL-18. Studies on IL-18 effects on chondrocytes further showed that it inhibits TGF-β-induced proliferation and enhances nitric oxide production. IL-18 stimulated the expression of several genes in normal human articular chondrocytes including inducible nitric oxide synthase, inducible cyclooxygenase, IL-6, and stromelysin. Gene expression was associated with the synthesis of the corresponding proteins. Treatment of normal human articular cartilage with IL-18 increased the release of glycosaminoglycans. These finding identified IL-18 as a cytokine that regulates chondrocyte responses and contributes to cartilage degradation.
The localisation of Interleukin-1β-converting enzyme (ICE)/caspase-1 in human osteoarthritic tissues and its role in the maturation of interleukin-1beta and interleukin-18 have been shown by Saha et al. (1999). Saha et al. studied the expression and production of caspase-1 in human normal and osteoarthritic (OA) cartilage and synovium, quantitated the level of ICE in OA chondrocytes, and examined the relationship between the topographic distribution of ICE, interleukin-1β (IL-1β), and IL-18, as well as apoptosis of chondrocytes. The experiments performed in this study indicated that ICE was expressed and synthesised in both human synovial membrane and cartilage, with a significantly greater number of cells staining positive in OA tissue than in normal tissue. ICE production was preferentially located in the superficial and upper intermediate layers of articular cartilage. The production of mature IL-1beta in OA cartilage explants and chondrocytes was completely blocked by treatment with a specific ICE inhibitor, which also markedly diminished the number of IL-18-positive cells. The relationship between active IL-1beta and ICE suggests that ICE may promote OA progression by activating this proinflammatory cytokine, and that IL-18 may play a role in cartilage pathology.
Gracie et al. (1999) suggested a proinflammatory role for IL-18 in rheumatoid arthritis. Gracie et al. detected the IL-18 mRNA and protein within rheumatoid arthritis synovial tissues in significantly higher levels than in osteoarthritis controls. It was also shown that a combination of IL-12 or IL-15 with IL-18 induced the IFN-γ production by synovial tissues in vitro. Furthermore, IL-18 administration of collagen/incomplete Freund's adjuvant-immunized mice facilitated the development of an erosive, inflammatory arthritis, suggesting that IL-18 may be proinflammatory in vivo.
However, so far, apart from chemical compounds, only the blockade of TNFα and IL-1β by using soluble receptors or monoclonal antibodies have been shown to decrease murine collagen-induced arthritis (CIA, which is a mouse model for rheumatoid arthritis) (Williams et al., 1994), and were therefore suggested as a therapeutic for rheumatoid arthritis.
Dayer (1999) summarized the different and partially contradicting functions of IL-18. IL-18 is a pleiotropic interleukin having both inflammatory enhancing and attenuating functions. On the one hand, it enhances production of the proinflammatory cytokines like TNFα, therefore promoting inflammation. On the other hand, it induces the production of NO, an inhibitor of caspase-1, thus blocking the maturation of IL-1β and IL-18, and possibly attenuating inflammation. This ambiguous role of IL-18 seriously questioned the efficacy of IL-18 inhibitors in inflammatory diseases. Furthermore, because of the interaction of a huge variety of different cytokines and chemokines in the regulation of inflammation, it could not have been expected to obtain a beneficial effect by blocking only one of the players in such a complicated scenario.